Identification of biogenetic calcite and aragonite using SEM

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Photography of thin layered siltstones and silty marls at Crnika Beach, Island of Pag, Croatia (scale: geol. hammer 33cm) – for more information see the paper by Bulić & Polšak (this Vol.)
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Published: Oct 6, 2009
DOI: https://doi.org/10.4154/GC.2009.15
Keywords:
Calcite, aragonite, morphology, geochemical difference, Feigl’s staining method, SEM

Main Article Content

Željka Žigovečki Gobac
Department of Geology, Faculty of Science, University of Zagreb
Hrvoje Posilović
Department of Geology and Paleontology, Faculty of Science, University of Zagreb
Vladimir Bermanec
Department of Geology and Palaeontology, Faculty of Science, University of Zagreb

Abstract

Identification of calcite and aragonite is very important for studying different fossil or recent biomineralized skeletons. Problem occurs when scanning electron microscopy is used for studying calcite and aragonite present in the same part of skeleton. The same chemical composition of these two minerals produces the same contrast on SEM images. There are three possible ways how to distinguish calcite and aragonite in such mixture.

(1) It is possible to recognize the crystal habits of these two minerals, if the crystal faces are developed.

(2) Geochemical difference could be also important tool for distinguishing aragonite (containing large cations like Sr, Ba, or Pb) from calcite (containing small cations like Mg, Mn, Fe, Zn, or Ni). However, it is also possible that large cations remain in calcite crystal structure after phase transformation from aragonite to calcite.

(3) Last possibility in distinguishing calcite from aragonite is to use staining methods. There were different staining methods used for SEM analyses with different success. SUZUKI et al. (1993) successfully used Meigen’s staining method, but results provided by Feigl’s staining method were unsatisfactory. Failure of using Feigl’s staining method was caused by erroneous applying of used solutions.

 

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Article Details

Issue
Vol 62 No 3 (2009)
Section
Scientific note

Authors have copyright and publishing rights on all published manuscripts.

Author Biographies

Željka Žigovečki Gobac, Department of Geology, Faculty of Science, University of Zagreb

Institute of Mineralogy and Petrology Department of Geology Faculty of Science University of Zagreb Horvatovac 95 10000 Zagreb Croatia

Hrvoje Posilović, Department of Geology and Paleontology, Faculty of Science, University of Zagreb

Institute of Geology and Paleontology Department of Geology Faculty of Science University of Zagreb Horvatovac 102a 10000 Zagreb Croatia

Vladimir Bermanec, Department of Geology and Palaeontology, Faculty of Science, University of Zagreb

Institute of Mineralogy and Petrology Department of Geology Faculty of Science University of Zagreb Horvatovac 95 10000 Zagreb Croatia

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